This usually occurs then I shoot with with a Sony DSLM (A7II or NEX3N) and a vintage (long focal length) lens. I can be avoided by closing the aperture which leads to longer exposures.
My question is: What is the origin of this issue?
My guesses are that the curtain shutter works really at its limit for these short exposures, as the "shadow" always appears one long edge of the image, or the the sensor is exposed to different amounts of light, due to the influence of a lens hood and the wide aperture.
EDIT: I was able to observe this behaviour again and gathered more information:
- The shadow always occurs on the top edge of the image (bottom edge of the sensor?) referring to the camera in landscape orientation.
- It also occurs independently from the direction of incident light.
- Removing the lens hood has no influence on the phenomenon.
So if we are talking about heavy vignetting, why is it so asymmetric?